LAUSR

High-quality perovskite films with large grains and long carrier lifetime are crucial for efficient solar cells. It is a simple and effective way to increase the perovskite grain size by adding some additives in the precursor solution. Here, we use a low-toxicity and low-volatility organic compound of 1-ethyl-2-pyrrolidone (NEP) as an additive in the PbI2(PbBr2)/dimethylformamide precursor solution to form a Lewis adduct of PbI2·NEP, which facilitate forming perovskite intermediate embedded with NEP molecules. The residual NEP molecules are kept in the narrow space between the intermediate film and substrate during annealing by using a closed-steam annealing method, which prolong the dissolution-recrystallization process. With assistance of the residual NEP, high-quality perovskite films with smooth surface, PbI2 free, high crystallinity, large columnar grains, and long carrier lifetime are fabricated. Correspondingly, the power conversion efficiency of the best perovskite solar cells is enhanced signific...